Synchronizing apparatus



M. ARTZT smcunomzme APPARATUS Filed June 21, 1939 MOTOR 2 Shoets$heet 2ARMATURE i 5 i g SYNCHRONIZING /9 TONE INPUT COMMUTATOR SYNCHRON/ZINGSYNCHRON/Z/NG A 7 58 TONE INPUTY MOTOR ARMATl/RE 55-55 ggf g 6/ 5 :3

.my. a Mom/2 ARMATURE 79 smcmzolwz/Ale 77 rams INPUT SERIES /82 FIELDINVENTOR. mun/c5 ARTZT ATTORNEY.

Patented Feb. 4, 1941 PATENT OFFICE SYNCHRONIZING APPARATUS MauriceArtzt, Haddonfield, N.

1., assignor to Radio Corporation of America, a ccrporationcf DelawareApplication June 21, 1939, Serial No. 280,303

11 Claims.

My invention relates in general to synchronizing apparatus, and moreparticularly to a method of, and apparatus for, synchronizing movingmechanical members or systems.

The synchronizing device, which is hereinafter described, has. been usedin actual practice to synchronize the operation of a facsimile scannerand receiver. It should be borne in mind, however, that this system isequally adaptable to 3 other related problems, and in no way do Iconsider myself to be limited to its use only with facsimile apparatus.

There are a number of fields of activity in which the operation of primemovers, such as 5 electric motors, in synchronous relationship with eachother is desirable. Accordingly, it is one of the objects of myinvention to provide a device which will accurately synchronize themovement of such motors.

In the field of facsimile transmission and reception, it is imperativethat the receiver move in synchronism with the scanner. The problem ofsynchronizing a recorder with a scanner can be divided into two parts.The first is the supply at the receiver of a reference frequency. The

reference frequency may come from a local circuit such as a tuning fork,or it may be receivedfrom the scanner by the channels by which thesignal representing the picture to be recorded is 0 received. The secondpart of the problem is the synchronizing of the driving means with thereference frequency. Accordingly, it is another of the objects of myinvention to provide a device which will utilize the reference frequencyto control apparatus which will definitely-and accurately maintain afacsimile recorder in synchro nous operation with a scanner.

One of the objections to some types of presently known systems ofsynchronizing is the fact to that relative complex and sensitiveapparatus is necessitated. It is another object of my invention toprovide a device which will be relatively simple, accurate, and easy tomaintain in adjustment. to Other objects will be apparent to thoseskilled in the art from a reading of the specification o the apparatusand its operation.

The operation of my apparatus in general is as follows: It has beenbrought out that this sys- 50 tern, as explained hereinafter, has beendirected toward the problem of synchronizing the opera tion of arecorder facsimile transmitter and recorder or receiver. In general,.the picture to be transmitted is fastened on a rotating drum, andscanning apparatus linearly measures the light (01. PIS-69.5)

values of the complete picture. Signals representative of the opticalvalues measured are transmitted, and these signals are used -to actuaterecording means at the receiver to reproduce the image. The recordingmaterial is mounted on 6 a picture drum, and it will be readily apparentthat for true reproductions, the recorder drum must operate insynchronism with the transmitter drum, that is to say, the two drumsmust operatenot only with equal speeds but in a co- 10 phasalrelationship. There are also other types of scanning such, for instance,as the so-called rocker arm type'of scanning, but it will be appreciatedthat the apparatus disclosed hereinafter will be equally adaptable tothese types of scanning and recording since the prime movers which drivethe devices must be maintained in synchronous operation.

This system presupposes there will be made available at the receiver asynchronizing tone which accurately indicates the speed of thescanningsystem. This can be received by radio as a tone generated by thescanner motor, or if the scanner is held at some fixed speed by tuningfork control, a similar fork can supply this tone 2 at the recorder.

At the receiver is used a motor, which in general practice, although notnecessarily, has been a shunt wound direct current motor. Connected tothe picture drum is a commutating device 3i which is comprisedalternately of conducting and non-conducting segments. This commutatoris connected in shunt with the anode-cathode path of a gaseous dischargedevice, which in general comprises a gas filled thermionic vacuum tube.Accordingly, when a conducting portion of the commutator is engaged, thetube is short circuited from anode to cathode, and thus is extinguished.In addition, a resistance device is connected in the supply circuit ofeither the armature or the shunt field of the motor or both, and is alsoconnected across the anode-cathode path of the tube. When the tube isconducting,

a definite lower potential drop is developed across the member than whenthe tube is non-conducting, and hence the voltage supplied either to thearmature of the driving motor or the shunt field, or both, is increased.Initiation of the discharge of the tube is accomplished by means of thesynchronizing signal and, in the case of a gas filled thermionic tube,this is easily accomplished by impressing the signals of properpotential onto the control grid of the tube. Once the discharge isinitiated, the control grid loses control of the discharge, and as longas there is a potential gradient of proper magnitude and polaritybetween the anode and the cathode of the tube, the discharge will beself-sustaining.

Accordingly, it will be seen that the following action takes place: Insynchronous operation, the commutator becomes so phased with respect tothe synchronizing tone that it does not shortcircuit the anode-cathodepath of the gas filled tube until after the receipt of a synchronizingsignal. In addition to shorting the anode-cathode path of the tube, thecommutator will also short the device across which a potentialhereinbefore referred to is developed. The synchronlzing signal which isreceived when the commutator is non-conducting causes the discharge tubeto conduct, and effectively shunts or parallels the series device thusincreasing the po-. tential supplied to the armature and field. Thedischarge continues for a period of time until the anode-cathode path ofthe discharge tube is short-circuited by the commutator and thedischarge ceases. However, at the same time the series device in themotor circuit is also short-circuited and, accordingly, 9. maximumpotential is then impressed on the armature and field of the motor. Thismeans then that beginning with the discharge of the tube and continuinguntil the commutator becomes non-conducting again, the armature and thefield of the motor have the potential impressed thereon at a maximum ornearly so, and for a period of time equal to the time from the beginningof the non-conducting section of the commutator until the beginning ofthe discharge of the gaseous discharge device, the potential impressedwill be a minimum determined by the resistance of the series device.Accordingly, the average voltage impressed on the armature and fieldwill depend on the relative length of time the series resistance isshort circuited by tube and commutator compared to the length of time itis not shorted by either. In coming up to speed, the commutator willcome to some phase position relative to the synchronizing signal atwhich the correct average potential will be maintained that will givesynchronous operation. Now, it the motor should slow down, this phasewill change so that the tube will discharge for a longer period of time,and as the short-circuiting of the series device by commutator is for asubstantially constant time, the over-all corrective time will beincreased. The average potential impressed on the armature and field ofthe motor will be increased, and hence the motor will tend to speed up.The reverse is true when the motor speeds up and the corrective time isshortened, hence the average voltage impressed on the armature and fieldof the motor is decreased and the motor slows down.

My invention will best be understood by reference to the drawings inwhich Fig. 1 represents one embodiment of my invention,

Figs. 2, 3 and 4 are explanatory curves, and

Figs. 5, 6, 7 and 8 are still further embodiments of my invention.

Referring to Fig. 1, there is shown one embodiment of my invention.There is illustrated a motor having an armature member 10 havingresistance ll illustrated as connected in series therewith, and a shuntfield I2 connected in shunt with said motor armature and series resistance H. A source of electrical energy supply is illustrated by thepositive and negative symbols, and this is connected across the terminalof the connection between the shunt field and the armature, and acrossthe terminal of a resistive member 13 connected serially with theresistance H and shunt field l2. Coupled to the armature is a drivingmember here illustrated as shaft member I4, which is adapted to rotatewith the armature, and coupled to the shaft member is a commutatormember having insulating section l5 and conducting section 16.Positioned so as to press against the outer periphery of the commutatorare two contacters I1 and [8.

A thermionic vacuum tube [9 is illustrated and comprises a gas filleddischarge device. It will be appreciated that' other types of gaseousdischarge tubes may be used sllch, for instance, as mercury vapor tubes,neon tubes, and the like. The tube l9 has its anode 20 connected to thecontact member H which is adapted to be held in contact with thecommutator member. The anode 20 is also connected to the terminal of thearmature l0 and resistance II. The cathode 2| of the gas filleddischarge device is connected to the contact member l8 and to theterminal at which the shunt field of the motor joins the resistor II. Itwill be appreciated therefore that the resistor H and the two contactmembers I! and I8, and the space charge path of the gaseous dischargedevice, are connected in parallel. The tube l9 also has a control grid22 which is connected to the cathode 2| through a resistor 23 andresistor 13. The synchronizing signal input is represented as beingdirectly across the resistance 23.

Referring to Fig. 2, there are shown explanatory curves to explain theoperation of the device shown in Fig. 1. In this figure, there is shownplotted against time as one co-ordinate, two sections, one of whichrepresents the potential impressed on the armature oi the motor and theother which represents the synchronizing tone. The operation is asfollows: The synchronizing tone is illustrated as a sine wave although afiat topped or peaked wave would be just as readily usable. Thesynchronizing tone is impressed across the resistor 23 of the gas filleddischarge device I9 and causes this device to conduct, the control gridat this time having control of the tube. When the positive half 24 ofthe synchronizing signal causes the tube to conduct, the resistance Itis effectively short-circuited by the anode to cathode circuit of thetube 19, and the armature potential is raised very nearly to maximumvalue. This-is illustrated by the dotted section 25 of Fig. 2, and itfurther is assumed i that the commutator is so positioned that at leastone of the contacts l1, I8 is in contact with ,an insulating section ofthe commutator. Even though the synchronizing tone signal goes negative,the control grid 22 of the tube having lost control of the discharge inthe tube, the discharge will continue until the plate potential of thetube is either interrupted or rendered negative. As the motor rotates,the contacts H and I8 both will come into contact with the conductingsegment l6 and will short-circuit the resistor ll. Thus the tube [9 isrobbed of plate potential and the tube ceases to conduct. However, whilethis is true, the resistor l I also is short-circuited by the commutatorso that the potential drop therein from the power supply is eliminatedand the motor armature has a potential value impressed thereon which isrepresented by the black solid section'26 of the curve of Fig. 2. It isat this time that the motor armature receives the maximumpotential, ofcourse assuming a steady source ofvoltage supply; The length of timethat the resistor H is short-clrcuited depends upon the speed of themotor armature, and when one of the contacters ,l'l or l8 leaves theconducting section l6 and impinges onto the insulating, section l of thecommutator, the voltage impressed on the motor armature will drop due tothe factthat no plate current can now flow in the anode circuit of thetube l9, and will not again flow in the tube until the receipt ofanother positive synchronizing signal. This is illustrated by the lowersolid section 21 of the curve of Fig. 2. This lower'solid section iscontinued on to the next position-of the commutator with respect to timein a solid line for the purpose of showing the effect purely of thecommutator conductor l6. although as a matter of fact the voltageimpressed'on the motor armature again will increaseat the point 2301'they curve of Fig. 2 when the tube I9 'again becomes conducting. Thus,it will be seen that the average voltage impressed on-the armature ofthemotor lies somewhere between the peak voltage represented at 25 and .theline 21, and is clearly indicated as e average.

Referring to Fig. 3, there is shown graphically what occurs when themotor armature Ill speeds .up. Upon receipt of the positive half of thesynture will rise as indicated atthe face 28 of the curve.

However, if the motor has speeded up, this means that with respect totime the conducting section l6 of the commutator will close the contactsi1 and I8 at an earlier time relatively to the beginning. of dischargeas illustrated by the forward face 29 of. the voltage curve shown as dueto the commutator action only. This means that the two sections of thevoltage rise, one of which is illustrated as a dotted section and theother of which is illustrated as a solid section will be brought closertogether so-to-speak, or the overall time between-the interval t1 and t:is shortened. Since the tube '19 will not conduct until the receipt ofthe next synchronizing signal, this ineansthat the space between tz, orthe time at which the conducting segments leave one of the contacts I!or l8, and the time ta which is the time when the tube l9 begins toconduct, will be lengthened. This means that the average voltageimpressed; on the armature is decreased, and hence the motorwill beslowed down.

Referring to-Flg. 4, there is illustrated the operation of thedevicewhen the. motor tends to slowdown. Upon receipt of a positive half 24 ofthesynchronizingsignal, the tube I9 will conduct as shown by the-leading face 30 of the dotted section of curve. zflhe motor havingslowed down, a longer period of time will elapse before the conductingsection 13 closes the contacts I! and I8 than in the case of synchronousoperation, as illustrated in Fig. 2'. This means that the time intervalt5 and ts will be much greater than when the motor is runningsynchronously. The effect is such as to separate the two sections of thecurve illustrated by the dotted portion and the solid portion so thatthe time interval between the time when the resistor ll ceases to beshortcircuited by the conducting segment l6 'and the time when platecurrent from the tube l9 flows through the resistance will be greatlyshortened. This means then that the average voltage impressed on themotor armature will increase, and

hence the motor will speed up. Thus, changes in loading, line voltage,or other factors tending to afiect speed of operation will causecorresponding phase shifts of the commutator with respect to thesynchronizing signals, and such phase shifts will automatically increaseor decrease the average armature potential in such a direction as tocorrect this phase shift and maintain synchronous operation since, forsynchronous operation, the average voltage is predetermfnable.

Referring to Fig. 5, there is shown an alternative arrangement whereininstead of shortcircuiting the gaseous discharge device during a portionof the time, the gaseous discharge device is rendered non-conductingduring this portion of the time of a cycle of operation by opening itsanode circuit. a The conducting segment I 6 thereof extends around thegreater portion of the periphery of the commutator and the insulatingsection I5 is comparatively small wtih respect thereto. The arrangementis the same as in Fig. l with the exception of the comparative sizes ofthe insulating section I5 and the conducting sec-. tion iii of thecommutator, and that the commutator is connected in series with the tubel9 rather than in shunt.

It should be noted in this figure that the contacters l1 and 18 areconnected serially with the anode-cathode output of tube [9 and thisseries circuit then connected in shunt with the resistor II. This meansthen that the anode 20 of the tube I9 is robbed of anode potential whenone of the contacters IT or l8 engages an insulating section l5 of thecommutator. The circuit of Fig. 1, however, has the advantage over thearrangement disclosed in Fig. 5 of being comparatively sparkless inoperation, whereas the disclosure of Fig. 5 is not entirely so.

Referring to Fig. 6, there is shown another embodiment of my invention.In this figure, the motor armature through appropriate driving means 3|is operatively associated so as to rotate the commutator, the latterhaving insulating sections 32 and conducting sections '33. A variableresistor 34 is interposed between one terminal of the shunt field 35 andone terminal of the motor 30. The gaseous discharge tube 36 has acontrol grid 31 onto which is impressed the synchronizing pulses throughthe transformer 38. The anode 39 of the tube is connected to one of thecontactors 40. The other of the contactors 4| is connected serially witha resistor 42 and this is joined to the terminal of the shunt field, thelatter being connected to the resistor 34. The other terminal of thearmature and shunt field are connected to gether and to the cathode 43of the tube 36. This means that the tube is conducting only as long asthe contactors and 41 both engage one of the conducting segments 33 ofthe commutator, since the contactors 40 and 4| are arranged to operateserially with the anode 39 of the tube 36.

In actual practice, the number of segments of the commutator isdetermined by the speed of the motor and the control frequency. If themotor is to run at 1800 R. P. M., and the synchronizing tone is 480cycles for instance, the number of conducting segments preferably usedhas been sixteen. The length of the segments is so proportioned to theinsulation between them that the anode circuit of the gaseous dischargetube is opened. long enough to de-ionize the tube and allow the grid toregain control of the anode current over each insulating space.

In operation, with the gaseous discharge tube drawing no current, theresistance 34 is so set and the supply line is a resistor 55.

that the motor runs slightly slower than 1800 R. P. M. and the value oiresistance 42 is adjusted so that with the gaseous discharge tubedrawing anode currents at all times, the motor runs faster than 1800 R.P. M. Operation at 1800 R. P. M. then demands that the tube draw anodecurrent only part of the time. It will be seen from the figure that whenthe tube is conducting, the shunt field current is partially bypassedthrough the tube. slow, the time interval elapsing during the receipt ofa synchronizing tone and the interval during which contactors 40 and 4!are on a conducting segment is increased, and as a consequence, aportion of the field current is by-passed through the gaseous dischargetube for a longer interval of time than is usual during synchronousoperation. As a result the average field current is less than when themotor isoperated synchronously, and this drop in field current tends tospeed up the motor. The reverse is true it the motor tends to run fast.Less of the conducting portion of the commutator will close thecontactors 40 and 4| after the grid of the tube 39 initiates dischargedue to the shifting forward of the phase between the commutator and thesynchronizing tone, and as a result the average field current will beincreased and, accordingly, the effect is to slow down the motor. It maybe seen that with proper choice of commutator spacings and proper choiceof resistors 34 and 42, a condition may be obtained in which wide linevoltages or load changes may be compensated for automatically and themotor held in synchronism with the control tone.

Referring to Fig. 7, there is shown still a further embodiment of myinvention. In this figure, the motor armature 50 is operativelyconnected to the drive member 5| which is adapted to rotate a commutatorhaving conducting sections 52 and insulating sections 53. The shuntfield 54 is connected directly across the armature circuit, andconnected serially between the motor One terminal of this resistor isconnected to the negative side of the supply line and the other terminalwhich joins the motor circuit is connected through a resistor 56 to theanode 51 of the gaseous discharge tube 58. The commutator has a commonbrush 59 connected to all of the conducting segments and a contactor 60is adapted to press against the periphery of the commutator andultimately come into engagement with the conducting segments 52. In thiscase; the common brush 59 is connected to the cathode 6| of the tube 58,and the other brush B0 is connected through an anode resistor 52 to theanode of the tube. Accordingly, both the armature and the shunt fieldare affected by the anode current of the tube 58. This results in lessof a tendency on the part of the driving motor to hunt. A resistor 63and a condenser 64 are shunted across the commutator in order to act asa spark suppressor. The synchronizing tone is impressed onto the grid 5501' the gaseous discharge tube 58 through the transformer 56.

Referring to Fig. 8, there is shown an embodiment of my invention foruse with a series woundtype of motor. In this case, the motor armature10 is connected operatively to a drive member H which in turn'isconnected so as to rotate a commutator having conducting sections 12 andinsulating sections 13. Two brush membels l4 and 15 are positioned so asto contact If the motor runs the commutator, and the brush 15 isconnected to the terminal at which the armature HI is connected to theseries field 16 of the motor. brush 14 is then connected to the anode 11of the gaseous discharge tube 18 through a resistor IS. The terminal ofthe series field l6 remote from the terminal which is connected to thearmature is connected to the negative side of the supply line and to thecathode of the gaseous discharge tube 18. The control grid 8| of thetube is connected to the cathode through the secondary of a transformer82, the primary of which is adapted to have the synchronizing toneimpressed thereon.

In this arrangement, the operation is such that if the motor slows down,the average field current is lowered and the average armature current isincreased so that the effect is to speed up the motor. On the otherhand, if the motor speeds up the phase relation between the input toneand the conducting sections of the commutator are changed so that theaverage field current is increased and the average armature current isdecreased so that the eifect is to decrease the speed of the motor.Reference may be had to the explanation regarding Fig. 6 as to how thisis accomplished. If the arrangement as disclosed in Fig. 8 is used on analternating current series motor, the tube 18 could control only duringthe positive half of the supply cycle so that the armature would receivea maximum of onehalf the time through the tube and the field, and theother half of the time through the field only.

It will be appreciated that there may be departures from the exactdescription contained in this specification which will be within thespirit and scope of my invention, for example,-

such as the fact that the normal commutator of a D. C. motor may be usedas a substitute for the auxiliary commutator which has been described inthis specification.

It should be understood that by the term "synchronizing I mean toinclude not only the movement of two mechanical members at equal speeds,but also in a definitely maintained phase relationship.

What I claim is:

1. Apparatus for synchronizing the movement of the rotating element oftwo electrically driven motors comprising means operating under thecontrol of one of said motors for developing a recurring signalindicative of the position of the moving element of one of said motors,a source of energy supply for the other of said motors, resistive meansconnected to one of the electrical elements of the latter motor and tothe source of energy supply for said motor whereby at least a portion ofthe energy supplied to said latter motor traverses the resistance, andmeans responsive to the recurring signal and associated with saidresistive means for intermittently altering the energy traversing saidresistive means.

the position of the rotationg member comprising a source of power supplyfor the second of said motors, a resistor connected serially with themoving element of said second motor, and moving element of said motorand said resistor being connected in shunt across the power supply, acommutator having at least one conducting and one insulating segment,said commutator being driven by the moving element of said second motor,a gaseous discharge device having at least two of its electrodesconnected in shunt with at least a portion of the resistance, switchmeans connected in shunt to the discharge path of said gaseous dischargedevice, said switch means being so positioned as to be alternatelyopened and closed by contact with the conducting and non-conductingsections of the commutating member, and means responsive to saidrecurring signal for initiating current through the said gaseousdischarge device.

5. Apparatus in accordance with claim 4 wherein said gaseous dischargedevice comprises a gas filled thermionic tube.

6. Apparatus in accordance with claim 4 wherein said second motor is ashunt member, said shunt field being connected at one extremity thereofto the armature of the motor and connected at the other extremitythereof to the resistance member to a point on said resistance withoutthe portionthereof which is connected in parallel with the thermionicdischarge device.

'7. Apparatus for synchronizing the movement of a first and secondelectric motor and wherein said second motor is a shunt wound motorcomprising a-source of energy supply for said second motor, a resistivemeans connected serially with said motor armature and also said energysupply means, a commutating member having at least one conducting andone insulating segment, said commutating member being driven by saidsecond motor armature whereby i the position of the commutator isindicative of the position of the armature of the motor, a gaseousdischarge device having at least two electrodes thereof connected inparallel with said resistive means, a plurality of contactors eachelectrically connected to an electrode of said gaseous discharge devicesand connected in the anode-cathode circuit thereof, said contactorsbeing so positioned as to be rendered alternately conductive andnon-conductive by contact with a conducting or an insulating section ofsaid commutator, and means for initiating discharge in said gaseousdischarge device by means of the recurring signal.

8. Apparatus in accordance with 'claim 7 wherein said discharge devicecomprises a gaseous thermionic tube.

9. Apparatus in accordance with claim 7 comprising in addition, a timeconstant circuit connected in shunt across the contactors.

10. Apparatus for synchronizing the movement of a first and secondelectric motor wherein said second electric motor is a series woundmotor comprising means associated with said first motor for developing arecurring signal indicative of the phase of the rotating element, a

' source of energy supply for said second motor tion of the elementscomprising said commutator' is indicative of the position of said secondmotor armature, a gaseous discharge device having at least twoelectrodes, one of said electrodes being connected to one terminal ofthe source of energy supply, a pair of contactors adapted to engage withthe commutator and adapted to be alternately rendered conducting andnon-conducting thereby, one of said contactors being connected seriallyto the terminal of said motor where the series field and armature join,and the other of said contactors being connected serially with the otherof said electrodes of said gaseous discharge device, and means forinitiating discharge in said gaseous discharge device by means of saidrecurring signals.

11. Apparatus in accordance with claim 10 wherein said gaseous dischargedevice comprises a gas filled thermionic tube.

MAURICE AR'IZT.

